Thermoset polymers of strained ring polycyclic cycloolefins are extensively used for making molded structural articles. The preparation of these polymers, usually based on dicyclopentadiene, is known, for example, from U.S. Pat. No. 4,400,340, which describes a reaction injection molding (RIM) technique in which a reactant stream containing a monomer to be polymerized and a metathesis catalyst, and a second stream containing a catalyst activator and additional monomer are brought together in a mixing head and substantially immediately injected into a mold where the monomer polymerizes to form a shaped article matching the shape of the mold. The polymerization involves the opening of a cycloolefin ring, and the monomers are described as being metathesis polymerizable. The reaction is catalyzed by a transition metal catalyst such as a tungsten or molybdenum salt, preferably tungsten halide or tungsten oxyhalide, activated by an alkyl aluminum compound or other conventional activator compound. Details of the catalyst preparation are well known, for instance from U.S. Pat. No. 4,568,660. The gelation stage of the polymerization, unless the reaction is moderated to delay it, takes place almost instantaneously. Such polymers can also be molded from a single stream, using a modifier to delay the gelation stage of the pre mixed ingredients.
Poly(dicyclopentadiene) and the other metathesis polymerization products, although they are extensively crosslinked, retain the unsaturation of the monomer. Although the double bonds are rearranged by the polymerization, they provide numerous reactive sites for further modification, either during or after the polymerization, and involving increased crosslink density.
These polymer compositions obtained by metathesis polymerization combine relatively high values of impact strength and flexural modulus, compared to other polymers, and they are insoluble in common solvents such as gasoline, naphtha, chlorinated hydrocarbons, and aromatics. However, they have a relatively low glass transition temperature (T.sub.g), on the order of 125.degree. to 140.degree. C. for poly(dicyclopentadiene), and lack a desirable level of dimensional integrity or stiffness when subjected to an elevated temperature, that is, their "heat sag" performance level is low (by ASTM test 3769).
For many applications there is a need for thermoset polymers of norbornene-type monomers, such as poly(dicyclopentadiene), that have higher values of T.sub.g than any otherwise comparable thermoset polymeric materials, as well as a higher level of "heat sag" performance.